Heat exchanger

ABSTRACT

Inner and outer shells having plural channels therebetween form an annular heat exchanger.

INCORPORATION BY REFERENCE

This patent application incorporates by reference U.S. Pat. Nos. 6,293,338 to William I. Chapman et al., 5,797,449 to James I. Oswald et al., and 5,081,834 to Charles T. Darragh.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a device for exchanging heat. In particular, the invention concerns the mechanical arts and heat exchange between fluids.

2. Discussion of the Related Art

Since before Hero built his steam engine in the first century AD, devices for exchanging heat between non-contacting fluids have been known. Uses for these devices have multiplied and they are widely known today. For example, current day heat exchangers have many important applications including those in industry, such as petrochemical refining, in appliances, such as laptop cpu coolers, and in reciprocating engine cooling, such as radiators. Despite this long and successful history of heat exchanger development and use, there remain many heat exchanger applications without a viable heat exchanger solution. Among the applications in need of heat exchanger solutions are those involving small gas turbines including engines in the 1000 watt to 10,000 watt power output range.

SUMMARY OF THE INVENTION

In an embodiment, a heat exchanger assembly comprises an annulus formed by shells in substantially coaxial arrangement about an axis. The outer shell extends beyond each end of the inner shell and a plurality of closed channels having first and second open ends extend through the annulus. Each channel extends beyond each end of the inner shell. A first annular channel-sheet is circumferentially sealed with a first end of the outer shell and a first plurality of seals provides sealing for a plurality of first channel ends to a respective plurality of first channel-sheet openings. A second annular channel-sheet is circumferentially sealed with a second end of the outer shell and a second plurality of seals provides sealing for a plurality of second channel ends to a respective plurality of second channel-sheet openings. Plural channels are formed such that substantially involute shapes are described where the channels intersect an imaginary plane that is perpendicular to the axis. A plurality of the channels is for transporting a first fluid stream and a plurality of the spaces between adjacent channels is for transporting a second fluid stream. A second fluid stream path is a) directed substantially away from the axis and entering the annulus via a radial inlet located between first adjacent ends of the inner and outer shells, b) directed about parallel to the axis and through the annulus, and c) directed substantially toward the axis and exiting the annulus via a radial outlet located between second adjacent ends of the inner and outer shells.

In some embodiments, a first fluid stream path is directed substantially parallel to the axis, a plurality of passages have substantially involute cross-sections and are operative to transport a heat donor fluid, and a plurality of passages have substantially involute cross-sections and are operative to transport a heat recipient fluid.

In an embodiment, a heat exchanger assembly comprises an annulus formed by shells in substantially coaxial arrangement about an axis and the inner shell extends beyond each end of the outer shell. A plurality of closed channels have first and second open ends and extend through the annulus, each channel extending beyond each end of the outer shell. A first annular channel-sheet is circumferentially sealed with a first end of the inner shell and a first plurality of seals is provided for sealing a plurality of first channel ends to a respective plurality of first channel-sheet openings. A second annular channel-sheet is circumferentially sealed with a second end of the inner shell and a second plurality of seals is provided for sealing a plurality of second channel ends to a respective plurality of second channel-sheet openings. A plurality of the channels is formed such that substantially involute shapes are described where the channels intersect an imaginary plane that is perpendicular to the axis. A plurality of the channels are for transporting a first fluid stream and a plurality of the spaces between adjacent channels are for transporting a second fluid stream. A second fluid stream path is a) directed substantially toward the axis and entering the annulus via a radial inlet located between first adjacent ends of the inner and outer shells, b) directed about parallel to the axis and through the annulus, and c) directed substantially away from the axis and exiting the annulus via a radial outlet located between second adjacent ends of the inner and outer shells.

In some embodiments, a first fluid stream path is directed substantially parallel to the axis, a plurality of passages having substantially involute cross-sections are operative to transport a heat donor fluid, and a plurality of passages have substantially involute cross-sections and are operative to transport a heat recipient fluid.

In an embodiment, a heat exchanger assembly comprises an annulus formed by shells in substantially coaxial arrangement about an axis, a first end of the outer shell extending beyond a first end of the inner shell and a second end of the inner shell extending beyond a second end of the outer shell. A plurality of closed channels have first and second open ends and the channels extend through the annulus, the first end of each channel extending beyond the inner shell and the second end of each channel extending beyond the outer shell. A first annular channel-sheet is circumferentially sealed with a first end of the outer shell and a first plurality of seals is provided for sealing a plurality of first channel ends to a respective plurality of first channel-sheet openings. A second annular channel-sheet is circumferentially sealed with a second end of the inner shell and a second plurality of seals is provided for sealing a plurality of second channel ends to a respective plurality of second channel-sheet openings. A plurality of the channels is formed such that substantially involute shapes are described where the channels intersect an imaginary plane that is perpendicular to the axis. A plurality of the channels is for transporting a first fluid stream and a plurality of the spaces between adjacent channels is for transporting a second fluid stream. A second fluid stream path is a) directed substantially away from the axis and entering the annulus via a radial inlet located between first adjacent ends of the inner and outer shells, b) directed about parallel to the axis and through the annulus, and c) directed substantially away from the axis and exiting the annulus via a radial outlet located between second adjacent ends of the inner and outer shells.

In some embodiments a first fluid stream path is directed substantially parallel to the axis, a plurality of passages have substantially involute cross-sections and are operative to transport a heat donor fluid, and a plurality of passages have substantially involute cross-sections and are operative to transport a heat recipient fluid.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is described with reference to the accompanying figures. These figures, incorporated herein and forming part of the specification, illustrate the present invention and, together with the description, further serve to explain the principles of the invention and to enable a person skilled in the relevant art to make and use the invention.

FIG. 1A is a perspective view showing channels arranged between inner and outer shells to form an annular heat exchanger according to the present invention.

FIG. 1B is a cross-sectional view of a channel for use with embodiments of the heat exchanger of FIG. 1A.

FIG. 1C is a cross-sectional view of an interstitial space for use with embodiments of the heat exchanger of FIG. 1A.

FIG. 2 is a perspective view showing an exemplary channel having a curved cross-section for use with embodiments of the heat exchanger of FIG. 1A.

FIG. 3 is an end view showing a channel-sheet for use with embodiments of the heat exchanger of FIG. 1A.

FIG. 4 is a side view showing an inner shell within an outer shell for use with embodiments of the heat exchanger of FIG. 1A.

FIG. 5 is an exploded view showing heat exchanger parts for use with embodiments of the heat exchanger of FIG. 1A.

FIG. 6 is a perspective view showing an assembled heat exchanger in accordance with a “u” shaped flow path embodiment of the heat exchanger of FIG. 1A.

FIG. 7 is an illustrative diagram showing flow paths, including a “u” shaped flow path, of an embodiment of the heat exchanger of FIG. 1A.

FIG. 8 is a side view showing an assembled heat exchanger in accordance with an “n” shaped flow path embodiment of the heat exchanger of FIG. 1A.

FIG. 9 is an illustrative diagram showing the flow paths, including an “n” shaped flow path, of an embodiment of the heat exchanger of FIG. 1.

FIG. 10 is a side view showing an assembled heat exchanger in accordance with a “z” shaped flow path embodiment of the heat exchanger of FIG. 1A.

FIG. 11 is an illustrative diagram showing the flow paths, including a “z” shaped flow path, of an embodiment of the heat exchanger of FIG. 1A.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The disclosure provided in the following pages describes examples of some embodiments of the invention. The designs, figures, and description are non-limiting examples of certain embodiments of the invention. For example, other embodiments of the disclosed device may or may not include the features described herein. Moreover, disclosed advantages and benefits may apply to only certain embodiments of the invention and should be not used to limit the disclosed inventions.

FIG. 1A is a perspective view showing channels arranged between inner and outer shells to form an annular heat exchanger according to an embodiment of the present invention 100. An inner shell space 112 is enveloped by the inner shell. Included in the heat exchanger are a plurality of channels 106 and inner and outer shells 102, 104 arranged about a central heat exchanger axis x-x.

The channels 106 pass through a heat-exchanger annulus 103 formed between the inner and outer shells 102, 104 and a channel wall 126 of each channel bounds a channel cross-section 116 that is about normal to the axis x-x. In an embodiment, the inner and outer shells are cylindrical ad are coaxially arranged about the axis x-x.

A plurality of interstitial spaces 108 is formed between opposed walls of the channels 120, 124. The boundaries of these spaces 125 are about coextensive with respective opposed channel walls 120, 124 and opposed inner and outer shell segments 122, 123. As shown, these boundaries also describe, for each interstitial space, an interstitial cross-section 118 that is about normal to the axis x-x.

As will be understood by persons of ordinary skill in the art, the described heat exchanger structure provides a number of passages 106, 108 for conducting fluid streams. For example, heat transfer between first and second fluid streams at different temperatures is enabled by flowing the first fluid through the channels 106 and flowing the second fluid through the interstitial spaces 108.

FIG. 1B shows a channel cross-section 116. In various embodiments, the quantity and cross-sectional shape of the channels 116 is adapted to suit, among other things, the desired heat exchanger application and performance characteristics. In an embodiment, the channel cross-sections have inner and outer boundaries lying substantially along circumferential portions of the inner and outer shells 134, 136 and side boundaries lie substantially along radii describing the extremes of the circumferential portions of the inner and outer shells, 120, 140 (as shown).

FIG. 1C shows an interstitial space cross-section 118. The interstitial space cross-sections 118 have inner and outer boundaries lying substantially along circumferential portions of the inner and outer shells 122, 123 and side boundaries lying substantially along radii describing the extremes of the circumferential portions of the inner and outer shells 120, 124. Like the channel cross-sections above, these cross-sections might be described as somewhat “pie” shaped. However, channels and interstitial spaces have, in various embodiments, different cross-sections.

FIG. 2 shows a perspective view of a channel having a curved cross-section 200. Embodiments of curved channels 202 include those with simple curves such as those with “c” like cross-sections 204 (as shown) and complex curves such as those with “s” like cross-sections. In various embodiments, the curves are described by one or more radii of one or more dimensions. In an embodiment, the channel has a curved “c” like cross-section described by a varying radius. In an embodiment the channel cross-section has a generally involute shape. And, in an embodiment, the channel cross-section has opposed, curved sidewalls 208, 209 whose curvature is substantially defined by the involute of a curve.

In some embodiments channel-sheets are adapted to collect a plurality of flows transported by the channels and isolate these flows from one or a plurality of flows transported by the interstitial spaces. FIG. 3 shows an end view of an exemplary channel-sheet 300. This channel-sheet 302 is adapted to receive curved channels such as those of FIG. 2. A plurality of curved holes 304 in the face of the channel-sheet 308 interface with the ends of a respective plurality of curved channels 205. The curved holes have respective cross-sections 309.

Adjacent channel-sheet holes 304 bound opposed sides of interstitial spaces 306 such that the curved cross-section of the channels is substantially repeated in the shape of the interstitial space cross-section 307. In various embodiments, the interstitial spaces have circumferential inner and outer boundaries 320, 310 and each channel has inner and outer edge seals 322, 312 with respective circumferential boundaries. In various embodiments, edge seals are formed by abutment of adjacent parts, tongue and groove like features on adjacent or special purpose parts, weldments and the like.

Different embodiments of the heat exchanger 100 accommodate different flow paths. For example, FIG. 4 shows a side view of heat exchanger inner and outer shells enabling a “u” shaped flow path 400. Here, the heat exchanger outer shell length LO is greater than the heat exchanger inner shell length LI and the outer shell 402 extends beyond or overhangs, at both ends, the inner shell 406.

FIG. 5 shows an exploded diagram of selected heat exchanger parts 500. An outer shell 402 having enlarged end parts 404 a,b receives an inner shell 406 and forms an annular space 411 between the shells. A channel bundle 502 including a plurality of channels 202 is inserted in the annular space. Channel-sheets 302 a,b are inserted in the enlarged end parts where the ends of the channels 205 a,b are mated with peripheral channel-sheet holes 304 a,b and inner shell end parts 408 a,b are mated with respective channel-sheet central holes 303 a,b.

In various embodiments, interstitial spaces 306 are sealed along at least a portion of their length by contact between edges of the channels with inner and outer shells. In one example, outer shell end parts 404 a,b have a diameter larger than the central portion of the outer shell 405 to receive channel-sheets 302 a,b therein. This allows for a channel outer edge 210 to seal (along at least a portion of the channel) with an inside diameter of the central portion of the outer shell 504. Inner shell end parts 408 a,b have a diameter smaller than the central portion of the inner shell 409 to mate with a central hole in respective channel-sheets 303 a,b. This allows for a channel inner edge 211 to seal (along at least a portion of the channel) with an outside diameter of the central portion of the inner shell 506. As persons of ordinary skill in the art will understand, other sealing methods suited to the heat exchanger and application may be used.

FIG. 6 shows the heat exchanger of FIG. 5 after it has been assembled 600. FIG. 7 illustrates flow paths through the heat exchanger 700.

As seen from the exposed end of the heat exchanger 602 and FIG. 5, channel-sheets 302 a,b at opposite ends of the heat exchanger provide inlets and exits 304 a,b to the heat exchanger for a first fluid transported within the channels. In an embodiment, a first fluid is conducted from inlets 304 b to exits 304 a within a plurality of channels having respective paths 702 substantially parallel to the x-x axis.

Also seen from the exposed end of the heat exchanger 602 and FIG. 5, spaces between adjacent channels near opposite ends of the heat exchanger provide inlets and exits 604 a,b to the heat exchanger for a second fluid transported substantially between the channels. In some embodiments, intake and exhaust regions within and near each end the heat exchanger have radial boundaries lying substantially along inside edges of a plurality of channels 608 a,b. In an embodiment, a second fluid is conducted from radial inlets 604 a to radial exits 604 b along a path that is: directed substantially radially outward from the axis 704 a; then directed about parallel to the axis x-x 704 i; and, then directed substantially radially inward toward the axis 704 b. In some embodiments the first and second fluids flow in substantially opposite directions and in other embodiments the first and second fluids flow in substantially the same direction.

FIG. 8 shows a side view of an embodiment of the heat exchanger having inner and outer shells enabling an “n” shaped flow path 800. FIG. 9 illustrates flow paths through the heat exchanger 900.

Here, the length of a heat exchanger inner shell LI is greater than the length of a heat exchanger outer shell LO and the inner shell 406 extends beyond, at both ends, the outer shell 402.

This heat exchanger is similar to the one of FIG. 7 having, among other differences, differing relative lengths of the shells 402, 406 and channels 202. These different relative lengths provide for a different flow path through the spaces between the channels 307.

To either side of the outer shell 402, channels 202 protrude from an annular space between the inner and outer shells 411. At the ends of the heat exchanger, the channels are mated with respective channel-sheets 302 a,b having inlets and exits 304 a,b to the heat exchanger for a first fluid transported within the channels. In an embodiment, a first fluid is conducted from inlets 304 b to exits 304 a within a plurality of channels having respective paths 902 substantially parallel to the x-x axis.

Spaces between adjacent channels near opposite ends of the heat exchanger provide inlets and exits 804 a,b to the heat exchanger for a second fluid transported substantially between the channels. In an embodiment, a second fluid is conducted from radial inlets 804 a to radial exits 804 b along a path that is: directed substantially radially inward toward the axis 904 a; then directed about parallel to the axis x-x 904 i; and, then directed substantially radially outward from the axis 904 b. In some embodiments the first and second fluids flow in substantially opposite directions and in other embodiments the first and second fluids flow in substantially the same direction.

FIG. 10 shows a side view of an embodiment of the heat exchanger having inner and outer shells enabling a “z” shaped flow path 1000. FIG. 11 illustrates flow paths through the heat exchanger 1100.

Here, a heat exchanger outer shell 402 extends beyond an inner shell 406 at one end and the inner shell extends beyond the outer shell at the other. Where the outer shell extends beyond the inner shell, this heat exchanger is similar to the heat exchanger having a “u” shaped flow path of FIG. 7. Where the inner shell extends beyond the outer shell, this heat exchanger is similar to the heat exchanger having an “n” shaped flow path of FIG. 9.

At opposing ends of the heat exchanger 1002, 1004, channel-sheets 302 a,b provide inlets and exits 304 a,b to the heat exchanger for a first fluid transported within the channels. In an embodiment, a first fluid is conducted from inlets 304 b to exits 304 a within a plurality of channels having respective paths 1102 substantially parallel to the x-x axis.

A second fluid is transported in the heat exchanger in the spaces between the channels. At opposing ends of the heat exchanger 1002, 1004 spaces between adjacent channels provide inlets or exits 604 a, 804 b to the heat exchanger for a second fluid transported substantially between the channels. In an embodiment, the second fluid is conducted from radial inlets 604 a to radial exits 804 b along a path that is: directed substantially radially outward from the axis 1104 a; then directed about parallel to the axis x-x 1104 i; and, then directed substantially radially outward from the axis 1104 b. In some embodiments, the direction of the flow between inlets/exits 604 a, 804 b is reversed. And, in some embodiments the first and second fluids flow in substantially opposite directions and in other embodiments the first and second fluids flow in substantially the same direction.

Turning now to making the heat exchanger, materials of construction will be those suited, among other things, to the application where the heat exchanger will operate and the manufacturing process that will be used to make the heat exchanger. The heat exchanger materials of construction will have properties suited to heat exchanger operating temperatures and the fluids to be contained by heat exchanger parts. Other considerations include materials suited to desirable manufacturing processes such as rolling the inner and outer shells in some embodiments and using molten metal such as welding or brazing to join channel-sheets and channels and/or fashion seals in some embodiments.

Heat exchanger shells 102, 104, 402, 406, channels 106, 202 and channel-sheets 302 will frequently be made using metal and in cases using one or more metals. These metals include as steel, steel alloys such as stainless steel, copper, copper alloys such as brass, aluminum, nickel, titanium and other suitable metals.

In various embodiments, the heat exchanger parts are manufactured by suitable methods known to persons of ordinary skill in the art. In an embodiment, curved channels 202 are manufactured by drawing over a mandrel. And, in various embodiments, curved channels are fabricated using one or more curved surfaces as forms. For example, in an embodiment involute channels are fabricated from a paired involute curved surface formed by hydro pressing or magniforming individual sheets which are subsequently folded together, the closure edge (at the involute major diameter) being sealed by either lock seaming, brazing, or welding. This method of fabricating involute tubes is similar to that used to manufacture the flattened tubes used in automobile radiators.

Methods of manufacturing inner and outer shells 102, 104, 402, 406 include joining one or a plurality of sheets to form a circumferential shell. In an embodiment, sheet stock is formed, rolled and welded at a closure seam to make each shell. It should be noted that shell surface features including features aligned parallel to the heat exchanger axis x-x may be present in the shell sheet stock or may be added during or after manufacture of the shells. Features include tabs, ridges, corrugations, dimples and the like. Such features have purposes including enhanced heat transfer, seals, channel seals, channel supports, channel alignment and the like. In an embodiment, the shells have longitudinal corrugations for seating, supporting and/or sealing with inner and outer edges of the channels.

Channel-sheet 302 manufacturing methods include machining from stock or blanks and cutting and forming from sheet stock. In an embodiment, the sheets are fabricated from sheet stock, either by stamping in a progressive rotary die, or by magniforming. In some embodiments, the pierced holes have standing edges to provide for additional sealing or braze area or for a companion edge for welding the channels into the sheet.

Heat exchanger performance will in some embodiments be enhanced by modifying surface finishes. For example, in various embodiments channels 106, 202 will not have smooth interior and exterior surfaces. Instead, at least portions of these surfaces will have irregularities and/or dimensional changes to interrupt fluid boundary layers for the purpose of enhancing heat transfer. Processes suitable for creating irregular surface finishes include coining, peaning, embossing, dimpeling, ridging and similar processes known to persons of ordinary skill in the art.

Heat exchanger resistance to pressure differences including pressure differences arising from different fluid stream pressures is improved in some embodiments through the use of suitable pressure resisting devices. For example, surface finishes including use of the surface finish modifications mentioned above provide pressure resisting devices. In an embodiment, wavy contours on heat exchanger surfaces such as heat exchanger channels 106, 202 not only resist deformation urged by pressure differences, but enhance heat transfer.

In various embodiments, one or more channels 106, 202 have inserts including finned and corrugated parts to resist pressure urged deformation while enhancing heat transfer. Whether cast, formed from sheet, machined or made by another means known to persons of ordinary skill in the art, some embodiments of the channel inserts are fixed or partially fixed by bonding or mechanical constraint with respect to a surface of the channel. In yet other embodiments channel spacers tending to space apart adjacent channels along their length are used to resist deformation urged by pressure differentials. Such spacers are in some embodiments bonded to one or more channels and in some embodiments positioned by an independent structure such as a wire frame. Selection of a suitable pressure resisting device includes consideration of the heat exchanger performance, heat exchanger geometry and the characteristics of the fluids to which the heat exchanger is exposed, including fluid stream pressures.

In operation, a flow along a first heat exchanger path 702, 902, 1102 exchanges heat with a flow along a second heat exchanger path 704, 904, 1104. In an embodiment, the flows are in substantially the same directions and in an embodiment the flows are in substantially different directions. Either of the fluids may be the heat donor fluid cooled by the heat transfer process with the other fluid being the heat recipient fluid heated by the heat transfer process.

Heat exchangers in accordance with the present invention 100 have various applications including material processing applications such as in petrochemical facilities, equipment cooling applications such as fluid coolers in the food processing facilities and heat recovery processes such as recuperators for gas turbine engines. In each of these and other applications, persons of ordinary skill in the art will recognize herein a suitable embodiment(s) of the heat exchanger for the task at hand.

For example, in an embodiment the heat exchanger is applied to recuperating heat from a gas turbine engine. Here, gas from the engine's power turbine is exhausted into one of the flow paths in the heat exchanger, either the flow path inside the channels or the flow path between the channels. This hot engine exhaust is the heat “donor fluid.” Exhaust gas heat is transferred across the channel walls to a cooler fluid in the other heat exchanger flow path. This cooler fluid, typically air, is drawn through the heat exchanger by the gas turbine compressor.

While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example only, and not limitation. It will be apparent to those skilled in the art that various changes in the form and details can be made without departing from the spirit and scope of the invention. As such, the breadth and scope of the present invention should not be limited by the above-described exemplary embodiments, but should be defined only in accordance with the following claims and equivalents thereof. 

1. What is claimed is a heat exchanger assembly comprising: an annulus formed by shells in substantially coaxial arrangement about an axis, the outer shell extending beyond each end of the inner shell; a plurality of closed channels having first and second open ends; the closed channels extending through the annulus and each channel extending beyond each end of the inner shell; a first annular channel-sheet circumferentially sealed with a first end of the outer shell; a first plurality of seals sealing a plurality of first channel ends to a respective plurality of first channel-sheet openings; a second annular channel-sheet circumferentially sealed with a second end of the outer shell; a second plurality of seals sealing a plurality of second channel ends to a respective plurality of second channel-sheet openings; a plurality of the channels formed such that substantially involute shapes are described where the channels intersect an imaginary plane that is perpendicular to the axis; a plurality of the channels for transporting a first fluid stream and a plurality of the spaces between adjacent channels for transporting a second fluid stream; and, a second fluid stream path a) directed substantially away from the axis and entering the annulus via a radial inlet located between first adjacent ends of the inner and outer shells, b) directed about parallel to the axis and through the annulus, and c) directed substantially toward the axis and exiting the annulus via a radial outlet located between second adjacent ends of the inner and outer shells.
 2. The heat exchanger of claim 1 wherein: a first fluid stream path is directed substantially parallel to the axis; a plurality of passages having substantially involute cross-sections are operative to transport a heat donor fluid; and, a plurality of passages having substantially involute cross-sections are operative to transport a heat recipient fluid.
 3. A heat exchanger assembly comprising: an annulus formed by shells in substantially coaxial arrangement about an axis, the inner shell extending beyond each end of the outer shell; a plurality of closed channels having first and second open ends; the closed channels extending through the annulus and each channel extending beyond each end of the outer shell; a first annular channel-sheet circumferentially sealed with a first end of the inner shell; a first plurality of seals sealing a plurality of first channel ends to a respective plurality of first channel-sheet openings; a second annular channel-sheet circumferentially sealed with a second end of the inner shell; a second plurality of seals sealing a plurality of second channel ends to a respective plurality of second channel-sheet openings; a plurality of the channels formed such that substantially involute shapes are described where the channels intersect an imaginary plane that is perpendicular to the axis; a plurality of the channels for transporting a first fluid stream and a plurality of the spaces between adjacent channels for transporting a second fluid stream; and, a second fluid stream path a) directed substantially toward the axis and entering the annulus via a radial inlet located between first adjacent ends of the inner and outer shells, b) directed about parallel to the axis and through the annulus, and c) directed substantially away from the axis and exiting the annulus via a radial outlet located between second adjacent ends of the inner and outer shells.
 4. The heat exchanger of claim 3 wherein: a first fluid stream path is directed substantially parallel to the axis; a plurality of passages having substantially involute cross-sections are operative to transport a heat donor fluid; and, a plurality of passages having substantially involute cross-sections are operative to transport a heat recipient fluid.
 5. A heat exchanger assembly comprising: an annulus formed by shells in substantially coaxial arrangement about an axis, a first end of the outer shell extending beyond a first end of the inner shell and a second end of the inner shell extending beyond a second end of the outer shell; a plurality of closed channels having first and second open ends; the channels extending through the annulus; the first end of each channel extending beyond the inner shell; the second end of each channel extending beyond the outer shell; a first annular channel-sheet circumferentially sealed with a first end of the outer shell; a first plurality of seals sealing a plurality of first channel ends to a respective plurality of first channel-sheet openings; a second annular channel-sheet circumferentially sealed with a second end of the inner shell; a second plurality of seals sealing a plurality of second channel ends to a respective plurality of second channel-sheet openings; a plurality of the channels formed such that substantially involute shapes are described where the channels intersect an imaginary plane that is perpendicular to the axis; a plurality of the channels for transporting a first fluid stream and a plurality of the spaces between adjacent channels for transporting a second fluid stream; and, a second fluid stream path a) directed substantially away from the axis and entering the annulus via a radial inlet located between first adjacent ends of the inner and outer shells, b) directed about parallel to the axis and through the annulus, and c) directed substantially away from the axis and exiting the annulus via a radial outlet located between second adjacent ends of the inner and outer shells.
 6. The heat exchanger of claim 5 wherein: a first fluid stream path is directed substantially parallel to the axis; a plurality of passages having substantially involute cross-sections are operative to transport a heat donor fluid; and, a plurality of passages having substantially involute cross-sections are operative to transport a heat recipient fluid. 